Regularity of Erosion and Soil Loss Tolerance in Hilly Red-Earth Region of China

The observations from 14-yr long-term investigation on the soil-water losses in the sloping red-earth (slope 8°- 15°) showed that soil-water losses were closely correlated with land slope and vegetative coverage. Runoff rate in sloping red-earth could be reduced doubly by exploitation, while the soil erosion was enhanced doubly during the first two years after exploitation. Subsequently, it tended to be stable. Soil erosion was highly positively correlated with land slope, i. e. soil erosion increased by 120 t km-2 yr-1 with a slope increase of 1°. On the contrary, soil erosion was highly negatively correlated with vegetative coverage, i. e. soil erosion was limited at 200 t km-2 yr-1 below as the vegetative coverage exceeded 60%. Furthermore, soil erosion was highly related with planting patterns, i. e. soil erosion in contour cropping pattern would be one sixth of that in straight cropping. Based on the view of soil nutrient balance and test data, it was first suggested that the soil loss tolerance in Q2 red clay derived red-earth should be lower than 300 t km-2 yr-1.

Soil loss tolerance in the black soil region of Northeast China

Soil loss tolerance （/） is the maximum rate of annual soil erosion that is tolerated and still allows a high level of crop productivity to be sustained economically and indefinitely. In the black soil region of Northeast China, an empirically determined, default Tvalue of 200 （t/km2.a） is used for designing land restoration strategies for different types of soils. The ob- jective of this study was to provide a methodology to calculate a quantitative T for different black soil species. A field investigation was conducted to determine the typical soil profiles of 21 black soil species in the study area and a quantitative methodology based on a modified soil productivity index model was established to calculate the Tvalues. These values, which varied from 68 t/km2.a to 358 t/km2-a, yielded an average Tvalue of 141 t/km2.a for the 21 soil species. This is 29.5% lower than the current national standard T value. Two significant factors that influenced the T value were soil thickness and vulnerability to erosion. An acceptable reduction rate of soil productivity over a planned time period of 1% is recommended as necessary for maintaining long-term sustainable soil productivity. Compared with the cur- rently used of regional unified standard T value, the proposed method, which determines T using specific soil profile indices, has more practical implications for effective, sustainable management of soil and water conservation.

Quantifying the impacts of spatiotemporal land use and land cover changes on soil loss across agroecologies and slope categories using GIS and RUSLE model in Zoa watershed,southwest Ethiopia

Background Soil erosion in Ethiopian highlands is highly consistent with land use/land cover(LULC)changes that are associated with deforestation and a decline in biodiversity.However,identifying soil erosion-prone areas and quantifying soil loss in rugged terrains and various agroecologies due to LULC changes have not been dedicated to scientific studies.Therefore,we quantified the impacts of spatiotemporal LULC changes on soil loss across agroecologies and slope categories using GIS and RUSLE model from 1985 to 2021 in Zoa watershed,southwest Ethiopia.Moreover,prioritizing erosion severity risks at sub-watersheds and quantifying temporal sediment yield is essential for better conservation planning.Landsat images,rainfall,Digital Elevation Model,and soil data were obtained from field observations and secondary sources.Results Bareland and farmland have been expanding at the expense of other land use types.The annual soil loss in the watershed ranged from 0 to 113.21 t ha^(-1) year^(-1),0 to 163.16 t ha^(-1) year^(-1),and 0 to 194.58 t ha^(-1) year^(-1)with a mean annual soil loss of 21.07,29.35 and 40.93 t ha^(-1) year^(-1) in 1985,2000,and 2021,respectively.Among LULC classes,the highest soil loss was generated from bareland(31.73 t ha^(-1) year^(-1))and farmland(27.08 t ha^(-1) year^(-1))in 1985 later upsurged to 35.52 t ha^(-1) year^(-1)and 59.91 t ha^(-1) year^(-1) in 2021,respectively,due to the maximum susceptibility of soil erosion risks from unprotected surfaces.The results also revealed that the lowland agroecology generated the highest mean soil loss of 24.05 t ha^(-1) year^(-1)in 1985,39.74 t ha^(-1) year^(-1) in 2000,and increased to 57.55 t ha^(-1) year^(-1)in 2021.Considering the slope categories,the highest and most excruciating soil loss was engendered from steep(35.55–60.78 t ha–1 year–1)and very steep(52.48–72.69 t ha^(-1) year^(-1))slope terrains during 1985–2021.The northwestern part of the watershed is the most erosion-prone area which is now expanding to the central and western parts of the watershed.The sediment yield increased at the fastest rate at the watershed outlet,from 39.3%in 1985 to 94.26%in 2021.Conclusions The results of this study indicated that the conversion of other LULC categories into farmland was the most detrimental to a watershed in terms of soil loss,which necessitates the implementation of appropriate soil and water conservation measures with effective design by considering spatial variability to reduce soil erosion hazards.